rate my first uber team please :)

As you can probrably tell in the title, i am pretty new to pokemon so i was hoping to get some feedback on my team sorry if my explanations are kind of crap but i'm just beginning to learn most of the stuff xD

Arceus @ Silk Scarf
Trait: Multitype
Shiny: Yes
EVs: 252 Atk / 88 HP / 168 Spd
Adamant Nature
- Earthquake
- Shadow Claw
- ExtremeSpeed
- Swords Dance
Main physical sweeper of the team. self explanatory, very common sweeper to run on alot of teams. Shadow claw to counter ghosts who are immune to xtremespeed and speed EVs to boost the speed of the other skills up. I chose silk scarf over choice because in the case they have a ghost up and i have xtremespeed locked in it's pretty annoying.

Darkrai @ Leftovers
Trait: Bad Dreams
Shiny: Yes
EVs: 252 SAtk / 252 Spd / 4 SDef
Timid Nature
- Dark Void
- Dark Pulse
- Focus Punch
- Substitute
Open with dark void, if it is able to sleep the enemy pokemon i can then take out arceus and sword dance 1-2x and sweep as many as i can (unless they have counters but thats a different story) Couldnt really think of any other items, so i just put leftovers on him.

First, replace psychic with Psystrike on Mewtwo. It is the best move that Mewtwo ever got and basically allows him to mix sweep without compromising IVs.Timid nature should be used over modest. Ice Beam over Shadow Ball is also a very important move on Mewtwo, as it allows him to bypass stuff such as Landorus T and Groudon that can potentially go through Mewtwo. You are very weak to opposing Kyogres, I suggest putting Palkia or Latias in as one of the members in place of Tyranitar, since Tyranitar really does nothing to this team except set up sand, which this team benefits nothing from. Scarf Zekrom despite the fact that it cannot switch into Specs Kyogre works well in revenge killing Kyogres that aren't scarfed. It can also OHKO opposing Arceus if you run Adamant on Zekrom. You also need something that can set up Stealth Rock at least.

Honestly, this team does need a lot of improvements, but once improvements are made, I am sure that you will win a lot of battles to come.